1. Field of the Invention
The present invention relates to an optical information recording device, and more particularly, to an optical information recording device capable of correcting recording conditions in real time.
2. Description of the Related Art
In general, the recording of information on an optical information recording medium, such as an optical disk, is carried out as follows: record data is modulated in an EFM (Eight to Fourteen Modulation) manner or eight-to-sixteen modulation manner; a recording pulse is formed based on this modulation signal; and the intensity or irradiation timing of a laser beam is controlled based on this recording pulse, thereby forming recording pits on the optical disk.
In this manner, since the recording pits are formed by using heat generated by the irradiation of the laser beam, it is necessary to set the recording pulse in consideration of a heat accumulation effect or thermal interference. Therefore, in the related art, various parameters constituting the recording pulse are set in plural strategy formats for every kind of optical disk, and a strategy the most suitable for the recording conditions is selected from the plural strategies, thereby recording information on the optical disk.
This strategy depends not only on an individual device differences in optical information recording devices, such as a variation in the spot diameter of a pick-up device or a variation in the precision of a mechanism, but also on manufacturers of optical disks used for recording reproduction and the recording speed. Therefore, setting the optimal strategy is to improve recording quality.
Therefore, there has been proposed a method in which the strategies the most suitable for various optical disks manufactured by different companies are calculated, these strategies are previously stored in a memory so as to correspond to the respective manufacturing companies, the manufacturing company recorded on the optical disk is read when information is recorded on the optical disk, and the strategy the most suitable for the read manufacturing company is read out from the memory.
However, according to the above-mentioned method, the optimal recording can be performed on the optical disks of the manufacturing companies previously stored in the memory, but cannot be performed on optical disks of manufacturing companies that are not stored in the memory. In addition, when the optical disks of the manufacturing companies previously stored in the memory are different from each other in recording speed, the optimal recording cannot be performed.
Therefore, a method in which test recording is previously performed for every recording condition, and in which the optimal strategy is determined, based on this test recording, which makes it possible to cope with various optical disks, has been disclosed in the following related arts: JP-A Nos. 5-144001, 4-137224, 5-143999, and 7-235056. However, in the method disclosed therein, the test recording has to be preformed before information recording starts. Therefore, it is not possible to perform strategy correction at the same time as recording, and thus it is difficult to cope with a case in which the optimal conditions of the inner and outer circumferences of an optical disk are different from each other.
As a result, that is, an inner circumferential portion of an optical disk may be slightly different from an outer circumferential portion thereof in recording characteristics, and the recording speed of the inner circumferential portion may be different from that of the outer circumferential portion in a recording apparatus. Therefore, a difference in recording quality between the inner circumferential portion and the outer circumferential portion can occur. Thus, in order to solve the above-mentioned problem, a technique of reducing the difference in recording quality between the inner circumferential portion and the outer circumferential portion by adjusting the output of a laser has been disclosed in JP-A No. 53-050707. The above-mentioned related art also discloses a technique of automatically performing the optimization of the output of a laser by detecting a variation in the amount of light of an auxiliary beam, which is called OPC.
In the above-mentioned OPC, since a unit for adjusting power is provided, it is possible to calculate correction conditions using a statistical index, such as an asymmetric value, which makes it possible to perform real time correction in which correction is simultaneously performed with recording. However, when the width or phase condition of a pulse is corrected, it is necessary to detect the amount of deviation between a recording pulse and a pit formed on an optical disk. Thus, in the above-mentioned OPC, it is difficult to cope with the case in which the optimal conditions of the inner and outer circumferential portions of an optical disk are different from each other.
Therefore, in order to correct the pulse conditions in real time, it is necessary to detect the position or length of a pit at the same time when recording is performed. As an approach to cope with this, a technique of reproducing substantially the same place as a recording place has been disclosed in JP-A No. 51-109851. However, this technique is applicable to magneto-optical recording, but is hardly applicable to optical recording not using magnetism. That is, in the magneto-optical recording, since information is recorded by the variation of magnetism, the output of a laser is not modulated. However, in the optical recording, since information is recorded by modulating the output of a laser, there is a problem in that the modulation has an effect on a reproduction side.
Techniques to solve this problem have been disclosed in JP-A Nos. 1-287825, 7-129956, 2004-22044, and 9-147361. JP-A No. 1-287825 discloses a technique of separately irradiating laser beams to a non-recording area and a recording area, and of acquiring reproduction signals by performing division between the respective signals obtained by the irradiation. According to this technique, it is possible to correct the distortion of a reproduction signal waveform by modulating the intensity of a laser beam when information is recorded.
Further, JP-A No. 7-129956 discloses a technique of obtaining reproduction signals by canceling out a modulated output by a reverse-phase clock and a laser output properly amplified by auto gain control (AGC).
Furthermore, JP-A No. 2004-22044 discloses a technique of canceling out the distortion of a reproduction signal due to the waveform variation of a recording pulse by creating a signal corresponding to the waveform variation of the recording pulse using a delay inversion equivalent circuit.
Moreover, according to the techniques disclosed in the above-mentioned JP-A Nos. 1-287825, 7-129956, and 2004-22044, modulation components can be cancelled out by calculation in theory. However, these techniques have various problems in practical use from the viewpoint of the precision of cancellation or the speed of calculation.
Further, JP-A No. 9-147361 discloses a technique of detecting, in real time, the deviation of a recording state by inputting a delay pulse obtained by delaying a recording pulse, a gate signal obtained by inverting a modulated signal, and a reproduction pulse into a phase comparator.
However, according to the technique disclosed in the above-mentioned JP-A No. 9-147361, pits are reproduced when the recording laser is in a low outputstate. Therefore, when the output of a sub-beam is low, it is difficult to obtain a superior reproduction signal. In particular, in a structure in which sub-beams for reproduction are generated by branching a main beam for recording, when a branching ratio is 20:1 or 30:1, there is a problem in that the sub-beam does not have a sufficient output.
That is, in JP-A No. 9-147361, the branching ratio is set to 8:1, but the branching ratio tends to increase with an increase in the speed of recording. In addition, the output of the beam is generally 1 mW or lower when the recording laser is in the low output state. Therefore, the intensity of light reflected from a recording surface detectable when the recording laser is in the low output state becomes extremely weak. When the intensity of detectable light is weak, the light can be easily affected by a circuit noise, a media noise, etc. As a result, a superior detection signal is not obtained.